SB 10.30.42
tato ’visan vanam candra
jyotsna yavad vibhavyate
tamah pravistam alaksya
tato nivavrtuh striyah
Translation:
In search of Krsna, the gopis then entered the depths of the forest as far as the light of the moon shone. But when they found themselves engulfed in darkness, they decided to turn back.
Purport:
The gopis entered a part of the forest so dense that even the light of the full moon couldn’t penetrate it. This scene is also described in the Visnu Purana:
pravisto gahanam krsnah
padam atra na laksyate
nivartadhvam sasankasya
naitad didhiti-gocarah
“One gopi said, ‘Krsna has entered such a dark part of the forest that we cannot possibly see His footprints. Therefore let us turn back from this area, which even the light of the moon cannot reach.’”